Great question. SeaGypSea, your iPhone is fine and is doing exactly what it is programmed to do. Ever since iOS 11 and then into iOS 12 and now in the current iOS 13, the new method of saving photos is HEIC. It is commonly known as High Efficiency Image File. The idea behind it is to streamline the size of the photo file and yet be able to maintain the original quality of the image. This way the user can get more files on the iPhone's storage. Those are the advantages.
The drawback is that PC running windows do not natively convert the files to Jpeg for use widely. The Windows user ends up manually converting the photo files. Several ways to do it and methods are listed once a Google search is performed.
Long story short- If you would like your iPhone to save photos in standard Jpeg format then do the following-
Go To Settings-->>Camera-->>Formats and then Select Most Compatible
Hope that helps.
Axel F.